Read this article at

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

This paper reports results obtained from a surface (both visually clean and dirty/dusty
surfaces) and active (aggressive or activated) air testing scheme on 140 residential
rooms in England, without visible water damage or mould growth, along with a few rooms
with visible mould growth/water damage tested for comparison purposes. The aim was
to establish normal background levels of mould in non-water-damaged interiors to benchmark
a ‘normal’ indoor environment, and in turn when there is a need for further investigation,
and, possibly, remediation. Air and surface mould was quantified based on the activity
of β-N-acetylhexosaminidase (EC 3.2.1.52; NAHA). The obtained readings showed a log-normal
distribution. Ninety-eight percent of the samples obtained from visually clean surfaces
were equal to or less than 25 relative fluorescence units (RFU), which is suggested
to be the higher bound for the range which can be used as a success criterion for
surface cleaning/remediation. Of samples obtained from visually dirty/dusty surfaces,
around 98% were below 450 RFU, which is suggested to define the lower-bound for abnormally
high levels of mould, rare even on dirty/dusty surfaces. Similarly, around 98% of
the air samples were found to have 1700 RFU or below. Values above 1700 RFU are therefore
deemed unlikely in a non-problem
indoor environment and can be indicative of a possible problem inducing mould growth.
The samples with values below 1700 were further divided into three proposed sub-categories.
Finally, the obtained RFU values and the suggested benchmarks were compared to those
obtained from 17 non-residential indoor environments tested previously in Copenhagen,
and the benchmarks that are currently used in Danish national standards, and they
were both found to be highly congruent, suggesting that local climate regimes and
room functions might not be as influential on indoor mould levels as commonly thought,
or that the nuances between England and Denmark in terms of these factors are not
strong enough to lead to sizable changes in the typical indoor mould levels in these
countries’ building stocks.

Fungi are ubiquitous components of indoor human environments, where most contact between humans and microbes occurs. The majority of these organisms apparently play a neutral role, but some are detrimental to human lifestyles and health. Recent studies that used culture-independent sampling methods demonstrated a high diversity of indoor fungi distinct from that of outdoor environments. Others have shown temporal fluctuations of fungal assemblages in human environments and modest correlations with human activity, but global-scale patterns have not been examined, despite the manifest significance of biogeography in other microbial systems. Here we present a global survey of fungi from indoor environments (n = 72), using both taxonomic and phylogeny-informative molecular markers to determine whether global or local indoor factors determine indoor fungal composition. Contrary to common ecological patterns, we show that fungal diversity is significantly higher in temperate zones than in the tropics, with distance from the equator being the best predictor of phylogenetic community similarity. Fungal composition is significantly auto-correlated at the national and hemispheric spatial scales. Remarkably, building function has no significant effect on indoor fungal composition, despite stark contrasts between architecture and materials of some buildings in close proximity. Distribution of individual taxa is significantly range- and latitude-limited compared with a null model of randomized distribution. Our results suggest that factors driving fungal composition are primarily global rather than mediated by building design or function.

Questionnaires are commonly used in epidemiologic studies to obtain information about house characteristics in order to predict the household aeroallergen exposure levels. However, the reliability of the predictions made with the questionnaires has not been evaluated. To address this issue, we compared objectively measured fungal propagules including the most frequently isolated mold genera (i.e., Alternaria, Aspergillus, Cladosporium, Penicillium, etc.) in a large sample of homes and compared these measured values to the questionnaire-determined household characteristics. As part of a prospective cohort study on the relation between residential allergen exposure and development of asthma in neonates, fungal air samples were collected from infant bedrooms and main living areas in 1000 homes in the Northeast USA, from December 1996 to January 1999. A Burkard portable air sampler was used in combination with DG-18 and MEA agars. A questionnaire was used to obtain information on host and house characteristics that may have an impact on the presence of fungal propagules in the air. This included information on observation of moisture problems (e.g., water leakage or damage, and mold or mildew growth), ventilation and heating facilities, building age and type, number of occupants, annual household income, presence of pets and pests, cleaning regimens, etc. The number of CFU/m3 air collected on MEA was significantly higher than on DG-18 (means, respectively, 1033.5 and 846.0 CFU/m3) (P < 0.0005). However, there was no significant difference between the numbers of CFU/m3 air collected from the main living area and from the infant bedroom. There was only a very weak relationship between the house characteristics, as described by questionnaire, and the presence of fungal propagules in indoor air. Only the temperature, relative humidity, season, and cats inside homes had a statistically significant impact on the presence of fungal propagules in indoor air. The presence of fungal propagules in indoor air cannot be reliably predicted by home characteristics. Actual measurements are required for fungal exposure assessment, and the use of only one medium to collect samples in one location in a home might be adequate to represent residential levels of fungi in indoor air.

Author notes

This is an open access article distributed under the terms of the Creative Commons
Attribution License (CC BY) 4.0
https://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, distribution and reproduction in any medium, provided
the original author and source are credited.